

<MudDataGrid T="Item" Items="Items" EditMode="@DataGridEditMode.Cell" ReadOnly="false">
    <Columns>
        <PropertyColumn Property="x => x.Name" />
        <PropertyColumn Property="x => x.SubItem.SubProperty" />
        <PropertyColumn Property="x => x.SubItem.SubItem2.SubProperty2" />
    </Columns>
</MudDataGrid>

@code {
    public List<Item> Items = new List<Item>()
    {
        new Item("A", "A-D", "A-D-E"), 
        new Item("B", "B-D", "B-D-E"), 
        new Item("C", "C-D", "C-D-E")
    };

    public class SubItem
    {
        public SubItem(string subProperty, string subProperty2)
        {
            SubProperty = subProperty;
            SubItem2 = new SubItem2(subProperty2);
        }

        public SubItem2 SubItem2 { get; set; }

        public string SubProperty { get; set; }
    }
    public class SubItem2
    {
        public SubItem2(string subProperty)
        {
            SubProperty2 = subProperty;
        }

        public string SubProperty2 { get; set; }
    }
    public class Item
    {
        public string Name { get; set; }

        public SubItem SubItem { get; set; }

        public Item(string name, string subProperty, string subProperty2)
        {
            Name = name;
            SubItem = new SubItem(subProperty, subProperty2);
        }
    }

}
